1. Field of the Invention
The present invention relates to a deformable intraocular lens which is inserted into the eye in place of the natural lens when the latter is physically extracted because of cataracts.
2. Description of the Related Art
It is generally accepted that when a cataract-impaired lens is surgically extracted, smaller incisions in the eyeball cause less chance of postoperative astigmatism.
Accordingly, a technique called KPE (Kelman's pharmacoemulsification; suction of lens substance crushed by ultrasonic emulsification) using an ultrasonic emulsification/suction apparatus has been developed. With this apparatus, an opaqued lens is crushed and emulsified by ultrasonication, and then sucked for removal. This technique permits an operation in which lenses are extracted through a small incision of approximately 4 mm, as compared to larger incisions of about 10 mm according to the conventional ECCE operation technique (extracapsular cataract extraction).
In connection with the technique which made small incisions possible as mentioned above, intraocular lenses which can be inserted through a small incision have been developed. Conventional intraocular lenses have an optical part made of a hard material such as glass or plastic; and, therefore, the incisions prepared at the time of transplant are greater than the diameter of the optical part which are in most cases 6.5 mm or more. Accordingly, even though a lens is extracted through a small incision according to the KPE technique, it is necessary that the incision be enlarged when a hard intraocular lens is inserted.
To solve this problem, Japanese Patent Application No. S58-1800S (Japanese Patent Application Laid-open (kokai) No. 146346/1983 Japanese Patent Publication No. H5-58748) discloses a deformable intraocular lens which can be inserted through a small incision made in an eyeball.
FIG. 4 (Prior Art) to FIG. 6 (Prior Art) show such an intraocular lens. It is made of an elastic material having predetermined memory characteristics. The thickness of the peripheral portion of the optical part of the lens is smaller than that of the central portion, and anchors 4a of a plurality of supports 4 which hold the optical part 3 within the eye and which are made of a different material from the optical part 3 are embedded at two positions on the periphery of the optical part 3 for bonding the supports to the optical part. The optical part 3 is integrally formed with a lens 3b which has an increased thickness from the periphery toward the center and a thin annular peripheral portion 3a which surrounds the lens 3b.
The optical part 3 can be deformed by rolling, bending, extending or folding to reduce its size. Therefore, an intraocular lens having such an optical part can be inserted through a small incision prepared in the eyeball with a newly developed applicator which can deform the optical part. With this applicator, the intraocular lens can be inserted through a small incision of about 4 mm in diameter, and can be restored to its original larger shape within the eye, based on the memory characteristics of the optical part 3. Thus, neither the size of the intraocular lens itself nor the method of inserting the lens requires the creation of a large incision.
In order to carry out an insertion of the above-described intraocular lens through a smaller incision using an applicator, the size of the object to be inserted, i.e., the deformable intraocular lens, is preferably as small as possible. In particular, the optical part, which affects the ease of the deforming operation, is desired to be minimized in size by making the thickness of the central part of the optical part smaller, and it is desired to reduce the size of the applicator by achieving a smaller thickness of the central portion.
In the conventional deformable lenses as described above, however, when the thickness of the center of the optical part is reduced, the periphery thereof becomes thinner accordingly. This is unfavorable because the anchors of the supports have to be embedded in a thin periphery portion of the optical part, which causes weak bonding strength between the supports and the optical part, poor supporting power of the supports, and reduced pull-off strength of the anchors. Thus, improved deformable intraocular lenses are still desirable.